Lyme disease is a multisystem illness caused by infection with the spirochete Borrelia burgdorferi and it is the leading vector-borne disease in the United States. Lyme disease is also common in Europe (mainly middle Europe and Scandinavia) and also occurs in Russia, China and Japan. In humans, B. burgdorferi infection causes infection primarily in the skin, nervous system, heart and joints. Lyme disease can usually be treated successfully with antibiotic therapy, with the best results seen in patients with early disease. Unfortunately, some patients may not have a complete response to therapy. We currently have two clinical protocols studying patients with Lyme disease. Both protocols are natural history studies and serve as the basis for multiple lines of investigation. One protocols addresses patients with post treatment Lyme disease syndrome. The other protocol allow for the study of patients with classical Lyme disease. Our work has addressed 3 areas in Lyme disease: laboratory diagnosis, clinical manifestations and immunological responses to B. burgdorferi. Regarding laboratory diagnostics, we have focused in developing better tests for both diagnosis and for persistence of infection. We collaborate with Dr. Mario Philipp and his group at Tulane University Medical Center, in the development of the C6 peptide ELISA. This test is simple to perform and is highly sensitive and specific. An important advantage of this test is that it can be used to diagnose Lyme disease in patients who have received the Lyme disease vaccine, and it can be used in Europe, where Lyme disease may be caused by B. garinii and B. afzelli. We also collaborated with the CDC to evaluate the C6 antibody response, as well as the antibody response to other recombinant antigens and synthetic peptides, in comparison with the 2-tier testing. When used alone, the C6 ELISA had similar sensitivity to 2-tier test. Moreover, when used in combination with the detection of IgM antibodies to a ten-amino acid peptide found at the C-terminus of most OspC proteins (pepC10), the combination had significantly higher sensitivity for diagnosing exposure to B. burgdorferi in patients with acute Lyme disease. Besides the use of the C6 antibody response for diagnosis of Lyme disease, we are currently evaluating this response as a possible marker for clearance of infection. Our results showed that the amount of antibody against C6 declines after successful antibiotic therapy of Lyme disease. These results suggest that a change in the anti-C6 antibody titer may serve as an indicator of therapy outcome for patients with acute and disseminated Lyme disease. Patients with post treatment Lyme disease syndrome participating in a double-blind placebo controlled trial of antibiotic therapy had very low levels of C6 antibody and there was no correlation between a decline of C6 antibody titer and clinical outcome. Further studies with more patients are needed to clarify how the test may be used in the clinical setting. Regarding immunological responses, in collaboration with Dr. Roland Martin (Neuroimmunology Branch, NINDS), we are studying the specificity repertoires and function of Borrelia burgdorferi-specific T cell clones using a novel methodology to decrypt the antigen specificity of T cell clones. In follow up to this study, we developed a highly specific and sensitive technique to track single T cell clones through the detection and quantification of T cell receptor (TCR) alpha or beta chain complementarity-determining region 3 transcripts by real-time RT-PCR. We examined the frequency of the candidate pathogenic T cell clones in the peripheral blood and cerebrospinal fluid (CSF) during the course of neurological disease. Using this approach, we detected variations of clonal frequencies that appeared to be related to clinical course, significant enrichment in the CSF, or both. We are also very interested in investigating the innate immune response to B. burgdorferi infection. We have examined the transcription profile of human peripheral blood mononuclear cells in response to B.burgdorferi lysate using oligonucleotide microarrays, as a basis for establishing new hypotheses regarding the molecular pathogenesis of Lyme disease. Regarding clinical manifestations, we have evaluated the audiological system in our patient cohort. These evaluations included studies with puretone sensitivity measurements, speech reception threshold, speech recognition, tolerance for speech and other studies of speech functions at high intensity presentation levels. It also included biomechanical studies of middle ear integrity and otoacoustic emissions to identify (or rule out) cochlear damage, and assessment of the auditory brainstem response to identify or rule out damage to the ascending auditory brainstem pathways. Our most significant finding was a reduced loudness tolerance in the presence of either normal or minimally impaired hearing.